Typewriting machines – Including interposed inking device for record-medium – Ribbon-feeding mechanism
Reexamination Certificate
1999-07-23
2001-01-16
Hilten, John S. (Department: 2854)
Typewriting machines
Including interposed inking device for record-medium
Ribbon-feeding mechanism
C400S225000
Reexamination Certificate
active
06174096
ABSTRACT:
TECHNICAL FIELD
The present invention relates in general to impact printers, and in particular, to a drive mechanism for the ink ribbon cartridge in such printers.
BACKGROUND INFORMATION
Impact printers using an ink ribbon to carry the printing medium from which characters on the printed page are formed must employ a ribbon drive mechanism to advance the ink ribbon so that fresh portions of the ribbon are available for printing. The mechanism driving the ribbon must accommodate manual tightening of the ribbon.
FIG. 1
illustrates an impact printer, printer
100
, in which the ink ribbon
104
is supplied in a ribbon cartridge, ribbon cartridge
101
. Printer
100
also includes a ribbon drive, ribbon drive
102
. Ribbon drive
102
may be a ribbon drive according to the prior art, or the ribbon drive of the present invention. A portion (see ribbon pinion
207
in
FIG. 2
) of ribbon drive
102
engages a spool (not shown) within ribbon cartridge
101
and advances the ink ribbon
104
. In order to manually tighten the ribbon
104
, ribbon cartridge
101
incorporates knob
103
, illustrated in the inset. By manually turning knob
103
in the same direction as the cartridge is driven, the ribbon
104
may be manually tightened. An enlarged view of such a ribbon-tightening knob is shown in FIG.
6
. Ribbon drive
102
must accommodate free rotation to permit manual tightening of the ribbon
104
while the ribbon cartridge is engaged with the ribbon drive
102
. This is complicated by the large speed reduction that is effected between the speed of the driving means for driving ribbon drive
102
, and the speed at which the ribbon
104
advances, which necessarily must be the rotation speed of an output of ribbon drive
102
.
Refer now to
FIG. 2
, in which is depicted a ribbon drive, ribbon drive
200
, in accordance with the prior art. Ribbon drive
200
includes ribbon motor
201
and gear mount bottom
202
, which supports gear
203
(shown in normal and inverted views), gear
204
(shown in normal and inverted views), and pinion gear
205
. These gears are enclosed by gear mount top
206
. Ribbon pinion
207
(which engages the spool (not shown) in ribbon cartridge
101
) passes through an opening
210
in gear mount top
206
and is coupled to pinion gear
205
, through which it is driven. Gear
203
, gear
204
, and pinion gear
205
effect the speed reduction between the speed of ribbon motor
201
and the speed of ribbon pinion
207
which drives the ribbon
104
. Because the speed at which the ribbon
104
advances is substantially slower than the rotational speed of ribbon motor
201
, the speed reduction produced through gear
203
, gear
204
, and pinion gear
205
is also substantial. Consequently, the torque that would need to be applied to knob
103
in order to manually tighten the ribbon
104
would be considerable unless a means were incorporated to decouple ribbon pinion
207
from pinion gear
205
. This is achieved in the prior art by the use of spring clutch
208
. When ribbon pinion
207
is rotated manually through its engagement with knob
103
, spring clutch
208
decouples ribbon pinion
207
and pinion gear
205
, and thereby the rest of the ribbon drive
200
. In this way, knob
103
and ribbon pinion
207
may be freely rotated, and the ribbon
104
manually tightened, without rotating the remaining portions of ribbon drive
200
.
Achieving the required speed reductions through the use of a gear train employing multiple individual gears, and a spring clutch to decouple the gear train from the ribbon pinion increases manufacturing and assembly costs and decreases reliability. Thus, there is a need in the art for an improved ribbon drive that incorporates fewer parts, thereby reducing manufacturing and assembly costs, and improving reliability.
SUMMARY OF THE INVENTION
The present invention addresses the previously mentioned needs by providing an improved ribbon drive that requires only four parts to achieve the requisite speed reductions as well as accommodating manual tightening of the ribbon. A worm gear which is rotated by a drive means further rotates a compound worm gear. The compound worm gear includes a pair of gear structures on a common shaft. One is a pinion gear that engages the worm gear, and the second is a worm which is rotated as the common shaft is rotated by the action of the worm gear on the pinion gear. The worm on the compound worm gear further engages a pinion gear on a pinion. The pinion then drives the ribbon cartridge. The compound worm gear is supported within a worm gear frame, through which the worm gear passes via an opening in the worm gear frame, in order to engage the pinion gear on the compound worm gear.
Manual ribbon tightening is accommodated through pivotal motion of the worm gear frame. The worm gear frame is free to pivot about the worm gear. When the worm gear is being rotated by the drive means, the engagement of the worm gear with the pinion gear on the compound worm gear tends to cause the compound worm gear also to rotate. Moreover, the force of the worm gear on the teeth of the pinion gear produces a moment which tends to cause the compound worm gear and the worm gear frame in which it is supported to pivot about the worm gear. This tendency to pivot on the part of the compound worm gear and the worm gear frame is restrained by the pinion. The worm on the compound worm gear engages the pinion gear on the pinion and the tendency of the compound worm gear to pivot acts to force the worm against the teeth of the pinion gear on the pinion.
The rotation of the compound worm gear, and hence the worm on the compound worm gear, then rotates the pinion. Rotation of the pinion then advances the printer ribbon. When the drive means is off, rotation of the pinion during manual tightening of the ribbon leads to a decoupling of the gear train in an analogous fashion, as will now be described.
With the drive means off, rotation of the pinion, and thereby the pinion gear attached thereto, forces the teeth of the pinion gear into the worm of the compound worm gear. This produces a moment about the worm gear. This moment in turn causes the compound worm gear to tend to pivot about that gear. The compound worm gear is supported in the worm gear frame, and thus, the worm gear frame also tends to pivot under the action of this moment. Because there is nothing to restrain this pivoting, the compound worm gear and the worm gear frame pivot away from the pinion. They will continue to pivot, at least, until the teeth on the pinion gear of the pinion no longer engage the worm on the compound worm gear. This effects the decoupling of the gear train that is necessary to accommodate the manual tightening of the tape. When the drive means subsequently is energized, the pivoting action previously described causes the worm on the compound worm gear to reengage the pinion gear on the pinion thereby rotating the ribbon.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention.
REFERENCES:
patent: 4376585 (1983-03-01), Fromme et al.
patent: 4651165 (1987-03-01), Shimada
patent: 4712931 (1987-12-01), Ohshima
patent: 5570606 (1996-11-01), Irie
patent: 5605071 (1997-02-01), Buchanan
patent: 5707159 (1998-01-01), Yamamoto et al.
patent: 5842795 (1998-12-01), Narita et al.
patent: 63-64785 (1988-03-01), None
Flynn John D.
Hilten John S.
International Business Machines - Corporation
Nguyen Anthony H.
Winstead Sechrest & Minick
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